A reciprocating compressor, for example, as shown in FIG. 10, is typically employed in air conditioners for automobiles and the like. This compressor has a pair of cylinder blocks 30 and 31 combined with each other. A swash plate chamber 32 is defined between these cylinder blocks 30 and 31. Housings 35 and 36 are attached to the outer end faces of the cylinder blocks 30 and 31 via valve plates 33 and 34, respectively. An intake chamber 37 and a discharge chamber 38 are defined between the valve plate 33 and the housing 35 and also between the valve plate 34 and the housing 36.
The drive shaft 39 is rotatably supported in these cylinder blocks 30 and 31. A swash plate 40 serving as a cam is fixed, in the swash plate chamber 32, to the drive shaft 39. Plural pairs of cylinder bores 41 and 42 are defined in the cylinder blocks 30 and 31 around the drive shaft 39. A double-headed piston 43 is housed in each pair of cylinder bores 41 and 42. Shoes 44, which serve as cam followers, are located between the swash plate 40 and each piston 43. Each shoe 44 has a sliding surface 45 that makes sliding contact with the front face or rear face of the swash plate 40 and a spherical surface 47 that makes sliding contact with a receiving recess 46 of the piston 43.
In the compressor described above, when the swash plate 40 is rotated with the rotation of the drive shaft 39, each piston 43 is reciprocated in the cylinder bores 41, 42 via the shoes 44 under the action of the swash plate 40. When the piston 43 is reciprocated, a refrigerant gas is introduced from the intake chamber 37 to the cylinder bores 41 and 42 as each piston 43 moves from the top dead center to the bottom dead center. Then, the refrigerant gas introduced into the cylinder bores 41 and 42 is compressed as the piston 43 moves from the bottom dead center to the top dead center and is discharged to the discharge chamber 38.
Generally, in order to increase the discharge capacity of a compressor, increasing the size of the cylinder bores 41 and 42 and increasing the sizes of the pistons 43, swash plate 40 and shoes 44 is contemplated. The pistons 43 and the swash plate 40 are generally made of a light aluminum alloy or the like. However, these members, which are made of the same metallic material, may seize. Accordingly, shoes 44 made of a ferrous metal are located between the pistons 43 and the swash plate 40 to prevent seizure between the pistons 43 and the swash plate 40. However, since ferrous metals have high specific gravity, the increase in the size of the shoes 44 increases the total weight of the compressor.
Assume that only the size of the pistons 43 and that of the swash plate 40 are increased, without changing the size of the shoes 44, in order to increase the discharge capacity. However, if the discharge capacity is increased, the load applied by the pistons 43 via the shoes 44 to the swash plate 40 is also increased. Accordingly, if the size of the shoes 44 remains unchanged, the load applied per unit area of the spherical surfaces 47 and that of the sliding surfaces 45 of the shoes 44 is increased. Consequently, the sliding resistance between the spherical surfaces 47 of the shoes 44 and the receiving recesses 46 defined in the pistons 43 and the sliding resistance between the sliding surfaces 45 of the shoes 44 and the swash plate 40 are increased.
If the sliding resistance between the spherical surfaces 47 of the shoes 44 and the receiving recesses 46 of the piston 43 is increased, the shoes 44 cannot move smoothly along the inner surfaces of the shoe retaining recesses 46. The shoes are moved by the swash plate 40 within the receiving recesses 46. If the shoes cannot move smoothly, the load applied between the sliding surfaces 45 of the shoes 44 and the swash plate 40 is increased, which further increase the sliding resistance between the sliding surfaces 45 of the shoes 44 and the swash plate 40.
In the compressor described above, a refrigerant gas is introduced from an external refrigerant circuit via the swash plate chamber 32 into the intake chamber 37. The refrigerant gas introduced into the swash plate chamber 32 cools each part in the swash plate chamber 32 and also prevents pulsation caused by the introduction of the refrigerant into the cylinder bores 41 and 42. However, R134a (CF.sub.3 CH.sub.2 F), which contains no chlorine, is employed as the refrigerant gas. This gas does not disrupt the stratospheric ozone layer. Chlorine is used as an extreme-pressure additive. An "extreme-pressure additive" is a substance that reacts with the surface of a metal and forms a metallic compound film to reduce frictional resistance. The refrigerant gas introduced into the swash plate chamber 32 washes off, by its own action, lubricant located on the surfaces of the swash plate 40 and other parts, so that lubrication between the shoes 44 and the pistons 43 and swash plate 40 is not easily achieved. In such cases, if chlorine, serving as the extreme-pressure additive, is not present in the refrigerant gas molecules, a great sliding resistance exists.
Therefore, it is an objective of the present invention to provide a reciprocating compressor that reduces the sliding resistance at the cam-piston joints.